[SOLVED] Safely modifying variable in two threads

Issue

Consider the following contrived examples-

Say I have a thread that modifies a global variable:

void thread_1(void* param) {
    for (int i=0; i<10; i++) {
        x += i; // x is global.
    }
}

And say I have another thread that modifies the same global variable:

void thread_2(void* param) {
    while (1) {
        x = 0; // x is global.
        usleep(20000);
    }
}

How do I pause the second thread's execution to wait until the first thread is finished executing to continue execution in the second thread safely to prevent a race condition from occurring?

Solution

If you want to create threads for example 6 threads you dont need to use 6 functions for that like you did , void thread1 and thread2.you must create them like :

pthread_mutex_t lock= PTHREAD_MUTEX_INITIALIZER;   // this locks the critical arrea
pthread_cond_t  consum = PTHREAD_COND_INITIALIZER; // and this is a conditional variable
    pthread_t consumerN[2];
    
    //then in your main function 
    int main(){
           
          
          pthread_create(&consumerN[1],NULL,thread_1,NULL);// go to thread_1
          pthread_create(&consumerN[2],NULL,thread_2,NULL);//go to thread_2
           
    }
    void thread_1(int *param){
       pthread_mutex_lock(&lock);
       pthread_cond_wait(&consum,lock);
       for (int i=0; i<10; i++) {
           x += i; // x is global.
      }
      pthread_mutex_unlock(&lock);
   }
   void thread_2(int *param){
       pthread_mutex_lock(&lock);
       pthread_cond_wait(&consum,lock);
       
      while(1){
          x=0;
          sleep(2000);


      }
      pthread_mutex_unlock(&lock);
  }

Answered By - gregni